1. Field of the Invention
This invention relates to a swing amount magnifying mechanism which can be utilized for, for instance, a lever dial gauge for displaying a swing amount of probe as a corresponding rotation amount of a pointer.
2. Description of Related Art
A swing magnifying mechanism is well known in the art, which transmits a swing amount of an arm with a probe provided thereon after magnification conversion through leverage to a different arm, and is utilized for a dial gauge or the like for magnifying a swing amount of a problem into a corresponding rotation amount of a pointer that is displayed.
Such a dial gauge can magnify even a slight swing amount with the magnifying mechanism into a great displacement of the pointer.
Japanese Patent Publication Laid-Open No. 6-109401 discloses a lever dial gauge, which has a construction as shown in FIGS. 13 and 14.
Referring to the Figures, reference numeral 1 designates a dial gauge casing, 51 a cover thereof, 11 a dial unit for displaying the rotation amount of a pointer, 41 a first arm, and 26 a second arm.
The casing 1 has a recess 2, a probe insertion hole 3 communicating therewith and open at one end of it, and a notch 9 formed in one edge wall of it defining the recess 2. The dial unit 11 is mounted in the notch 9.
The casing 12 further has a pair of integral bearing extensions 4A and 4B extending on the opposite sides of the probe insertion hole 3.
The first arm 41 is inserted through the probe insertion hole 3 such that a probe 31 extending from an end of it projects outward. The first arm 41 has a first shaft 5 provided in its intermediate portion and pivotally mounted via bearings 5A and 5B in the bearing extensions 4A and 4B.
The second arm 26 disposed in the recess 2 of the casing 1, can magnify the swing angle of the first arm 41, and has a pinion gear 23 and a crown gear 24 for transmitting the swing amount of the second arm 26 to the dial unit 11.
The second arm 26 is disposed adjacent to the first arm 41, which is inserted through the probe insertion hole 3. The second arm 26 has a second shaft 27 provided in its intermediate portion and pivotally mounted in a bottom portion 1A of the casing 1. The pinion gear 23 and crown gear 24 are mounted as a one-piece member for rotation in a bottom portion 1B of the casing 1.
The first arm 41 has movable surfaces 41A and 41B, which are formed on an inserted portion of the first arm 41 on the side of the first shaft 5 opposite the probe 31 and to be displaced with swinging of the first arm 41.
The second arm 26 has transmitting pins 28A and 28B, which are in contact with the movable surfaces 41A and 41B, respectively, of the first arm 41 and transmit a swing amount of the first arm 41 to the second arm 26. The second arm 26 further has a sector gear 25 provided at one end and in mesh with the pinion gear 23.
The second arm 26 is biased for rotation about the second shaft 27 in the clockwise direction in FIG. 4 by a string spring 29 provided in the recess 2. The movable surfaces 41A and 41B and the transmitting pins 28A and 28B are thus held in contact with one another at all times, i.e., irrespective of whether or not the swing amount measurement is in force.
In the lever dial gauge having the above construction, the mechanism for magnifying a swing amount of the probe 31 into a corresponding rotation amount of the pointer in the dial unit 11, will now be described with reference to FIG. 14.
When the probe 31 is caused to swing in direction U in FIG. 14, the first arm 41 is rotated about the first shaft 5 in the counterclockwise direction in FIG. 14, thus causing the movable surface 41B to be displaced downward in FIG. 14. With the downward displacement of the movable surface 41B, the transmitting pin 28B of the second arm 26 is pushed downward in FIG. 14, thus causing the second arm 26 to be rotated about the second shaft 27 in the counterclockwise direction.
The downward rotation of the second arm 26 is transmitted via the sector gear 25 of the pinion gear 23 to cause clockwise rotation thereof, and is also transmitted via the crown gear 24 to a center pinion 14, which is provided in the dial unit 11, whereby the swing amount is displayed as a corresponding rotation amount of the pointer 16 via a shaft 15.
When the probe 31 is caused to swing in direction D, the first arm 41 is rotated about the first shaft 5 in the clockwise direction in FIG. 14, thus causing this time the movable surface 41A to be displaced upward in FIG. 14. The transmitting pin 28A of the second arm 26 is thus pushed upward in FIG. 14, thus causing the second arm 26 to be rotated about the second shaft 27 in the counterclockwise direction, i.e., in the same direction as in the case of swinging of the probe 31 in the direction U.
In the lever dial gauge of this construction, the pointer 16 is thus rotated in a fixed direction irrespective of the direction of swinging of the probe 31.
In the above swing magnifying mechanism for magnifying a swing amount through leverage, the magnification factor varies with the fulcrum positions of the two levers and the distance between transmission points. The mechanism of magnification will now be described with reference to FIGS. 15 and 16.
FIG. 15 shows the position relation between the first and second arms 41 and 26 in the neutral state, i.e., a state without swinging of the probe 31. In this state, the first and second arms 41 and 26 both extend along a neutral line M connecting the first and second shafts 5 and 27, and the transmitting pins 28A and 28B on the second arm 26 are on the neutral line M.
The transmitting pin 28A is found at a position to internally divide the line segment L between the first and second shafts 5 and 27, that is, it is at distance RA1 from the first shaft 5 and at distance RA2 from the second shaft 27. The transmitting pin 28B is found at a position to externally divide the line segment L, i.e., it is at distance RB1 from the first shaft 5 and at distance RB2 from the second shaft 27. The distances RA1, RA2, RB1 and RB2 are related as RA2&lt;RA1&lt;L and RB2&lt;L&lt;RB1.
FIG. 16 is a simplified showing of FIG. 15, and shows a state when the probe 31 has swung by angle S in direction D.
The swinging of the probe 31 in the direction D causes the first arm 41 to be rotated about the first shaft 5 by angle S in the clockwise direction, thus causing the movable surface 41A of the first arm 41 to push and displace the transmitting pin 28A of the second arm 26 about the second shaft 27 by angle .theta. in the counterclockwise direction to a position above the neutral line M.
In this state, the swing angle S of the first arm 41 and the swing angle .theta. of the second arm 26 are related as
LA1.times.sin S=RA2.times.sin .theta.. PA1 Sin .theta..apprxeq..theta. PA1 LA1.times.S=RA2.times..theta. PA1 LA1 (.apprxeq.RA1)&gt;RA2,
So long as the angles S and .theta. are changed very slightly,
and Sin S.apprxeq.S.
and thus
and .theta.=K.times.S (K=LA1/RA2)
Since
the swing angle S of the first arm 41 is converted with magnification factor K into the swing angle .theta. of the second arm 26.
Although not shown in FIG. 16, we can obtain similar relations with the transmitting pin 28B, which becomes operative when the probe 31 is caused to swing in the direction U opposite to the direction D.
As described above, so long as the swing angles S and .theta. from the neutral line M are small, the magnification factor K, by which the angle S is converted into the angle .theta., is stable and fixed. As the angles S and .theta. are increased, however, the displacement of the transmitting pin 28A eventually becomes no longer negligible, that is, the magnification factor K is increased with increase of the angle .theta..
Particularly, when the transmitting pin 28A which is found at the point of the internal division of the line segment between the first and second shafts 5 and 27 becomes operative, an increase of the swing angle .theta. results in a great change in the magnification factor K as shown in FIG. 17 because the absolute distances RA2 and RA1 are small.
In order to prevent such great change in the magnification factor K, it has been attempted to improve the accuracy of the swing amount magnifying mechanism by reducing the rate of change in the distance LA1 with a change in the angle .theta. by setting the distance L between the first and second shafts 5 and 27 to be sufficiently large.
To set the distance L to be sufficiently large, however, dictates increasing the length of the first arm. This means that it is necessary to prepare a plurality of arms in advance for the dial gauge manufacture in dependence on the swing amount range of the probe. This gives rise to the problems of cumbersomeness increase and complication of parts management in manufacture and cost increase of manufacture of the first arm.
Moreover, increasing the length of the first arm dictates correspondingly increasing the sizes of the casing 1, cover 51 and other components of the dial gauge, thus posing the problem of dial gauge size increase and making the problems of the component management complication and manufacturing cost increase more serious.
The invention seeks to overcome the above drawbacks inherent in the prior art, and it has an object of providing a highly accurate swing amount magnifying mechanism with a combination of a plurality of levers, which can convert the swing amount of the probe with a fixed magnification factor without considerable component alteration when the swing amount range is increased.